This invention relates generally to an apparatus and method for inspecting glassware for the presence of tramp glass or fused glass and in particular to the inspection of glassware for the presence of tramp glass or fused glass on the inside bottom surface of the glassware. In order to ensure maximum consumer protection, it is desirable that all surfaces of a glass container be inspected for defects. These defects may take the form of checks, birdswings, tramp glass, fused glass, and many others. Various methods have evolved to inspect glassware for such manufacturing defects; however, the inventor is unaware of any method or apparatus for inspecting the inside bottom surface of glassware for the presence of tramp glass or fused glass. For the purposes of this invention, it is essential that checks be distinguished from tramp glass and fused glass.
Most glassware is manufactured to bear some indication of its origin by placement of certain mold markings on the outside base of the container. These markings may take the form of letters, numbers, or abstract designs. The presence of the various types of markings plus the fact that the same markings do not always appear in the same physical location has made inspection of glass bottoms inherently difficult. A discussion of a couple of the state-of-the-art devices may aid in appreciating the present invention.
There are light operative means for inspecting the "heel" area of glassware for checks. In one such apparatus the light is directed into the glassware and reflected therefrom (ideally) only when there is a check present. A check is a fracture line which normally occurs internal to the glassware and is not a surface defect. When the light strikes the check, the air-check layer causes the light to be reflected from the plane of the check. The reflected light is sensed and a reject signal generated to ultimately cause the subject ware to be discarded.
Another method for inspection of glassware with light is disclosed by U.S. Pat. No. 3,887,285. The invention is directed to inspection of flasks for checks occurring in the neck of the flask. Light is directed through the outer surface of the flask and focused onto the wall of the container opposite thereto and passes therethrough. The presence of a check causes the direction of the light to be significantly redirected and ultimately detected by a light sensing means.
The angle of incidence of the light is such that the light "enters" the wall of the glass container, i.e., the light is not reflected by the primary surface of the container. When the light strikes a check it is reflected from within the wall and emerges from within the wall to be sensed by a light sensor. The angles involved and the suspected angle of the check are critical since the angle of incidence, the angle of the check, and the resulting angle of reflection are all dependent.
Should the teaching of U.S. Pat. No. 3,887,285 be applied to the bottom of a container, the lettering, mold markings, or pertubations present on the bottom would cause reflections not indicative of errors. Additionally small imperfections such as seeds and blisters within ranges of acceptability would indicate defective ware.
It is an object of this invention to provide a method and apparatus for inspecting the bottom of glass containers for tramp glass or fused glass.
It is a further object of this invention to inspect such glassware by directing light through the outside walls of the glassware and onto the inside bottom surface of the glassware.
It is yet another object of the present invention to inspect such glassware by directing light onto the inside bottom surface in such a manner whereby substantially all of the light is reflected unless tramp glass or fused glass is present in the container.